Process of producing magnesium powder by cold rolling and grinding



Patented Aug". 31, 1948 UNITED s'rArEs PATENT OFFICE z,44a.24a

POWDER BY COLD GRINDING ROLLING AND Harold r. Anderson, Mountain View,Calif., as-

signonby mesne assignments, to

The Permanente Metals Corporation, a corporation of Delaware No Drawing.

'paumion June 15, 1944,

This invention relates to a process for treating magnesium metal toproduce powdered magnesium.

It is contemplated by this invention to produce powdered, or finelydivided, magnesium metal which may be used as flashlight powder, as anincendiary material for instance in fireworks or the like, or as achemical reagent.

Magnesium metal as obtained, for example, by the sublimation of metallicmagnesium or bythe reduction of magnesium containing ores with reducingagents which give, except for the magnesium, non-gaseous reactionproducts, is recovered in a condensing device in the form of crystalswhich deposit in agglomerat'e masses. The crystalline deposit soobtained is quite malleable, and it has been iound in practice that sucha deposit cannot be satisfactorily reduced to a powder by directintroduction into a hammer mill or other mechanicalreduction device.

It has accordingly been the ordinary procedure to reduce crystallinemagnesium to powdered form by casting into cylinders or ingots, millingthe ingots into shavings, and then running these shavings thru a hammermill or similar device.

Other processes have been devised for the production of magnesium powdersuch as directing a jet of gas against a stream-oi molten metal as thelatter is forced downwardly out 01' the lower part of a melting vessel,or volatilizing the metal in an inert gas and chilling with a stream ofcool gas to cause condensation of finely divided metal. In general,however, the cheapest, and most satisfactory method of making the powderhas been to cast, form shavings or other thin pieces from the cast mass,and subject the shavings to the action of a hammer mill. In all of thesemethods, the crystalline magnesium has been first subjected to a heattreatment and, in casting at least, with consequent rearrangement orre-alignment oi the crystals.

I have now discovered that the crystalline magnesium can be reduced topowder form by first flattening the crystallineagglomerates, ormechanically extending them along one general plane or axis, and thensubjecting the flattened metal to the action of a hammer mill or othermechanical reduction device. The flattening oi the metal evidentlycauses the crystals to become brittle and they are then. easily powderedby a pounding or beating action as effected by a hammer mill.

Advantageously the crystalline magnesium is rolled in the cold state andthen subjected to treatment by a hammering action, The coldrolled'crystal's are readily reduced to the pow dered state by hammeringin a hammer mill or the like. It is advantageous to cold roll thecrystals rapidly. Evidently distortion eflects are obtained in thismanner which enable the production of many cleavages and, thereby, theproducing ot 'a finely divided magnesium product.

It is an advantage oi my process that the number of steps in theproduction of magnesium powder from refined magnesium metals arereduced. It is a further advantage that mechanical losses 0! metal suchas are usually incurred in casting, shaving and other handling areavoided. It is a great advantage of my process that heating of themetal, with consequent dangers of loss by increased oxidation ornecessity for increased protection irom atmospheric action upon themetal, is avoided.

In my process the flattening, advantageously by cold rolling, and thehammering can be eiiected satisfactorily in thepresence of air. If it bedesired to prevent even small amounts oi! atmospheric degradation of themetal, the operations can be carried out in an inert atmosphere, as forexample by maintaining an atmosphere of hydrogen, argon or other inertgas about the rolls or mills, suitably housed, or the metal can beprotected during working by application of a surface coating of a liquidhydrocarbon, preferably a low gravity liquid hydrocarbon such askerosene or distillate.

As an example oi. the method of carrying ou my process, I use as astarting material magnesium produced by the reduction of magnesia with acarbonaceous reducing agent such as coke and subsequent refining of thecrude condensate by distillation to recover sublimed magnesium as 1crystals. The crystals deposit in the flnal stage as an irregular mass.This cooled crystalline mass is fed quickly thru a set of steel rolls.The rolled and flattened mass of magnesium is now run through a hammermill and the resulting powder is screened. The coarser particles areagain fed through the rolls and are put through the hammer mill againand these operations repeated once more to reduce the whole mess to asuitable state of subdivision.

The final product has the following fineness: It all passes a 10 meshscreen, 2% remaining on a 20 mesh screen, 46% on a 50 mesh screen, 29%

on an mesh screen, and'23% passes through 80 mesh. The product isexcellent as a flashlight powder, being ignited very easily when a smallamount of potassium chlorate is admixed therewith. 'It is useful inpowder metallurgical processes and it is also useful as a. component offlares and the like.

Alternatively, the crystalline magnesium may be pressed or hammeredflatprior to grinding or hammer milling. However, it is more convenient, andit is preferable to flatten the crystals by passing them quickly througha rolling operation. The more quickly the crystals are flattened, ormechanically extended along one plane or axis, the greater are thedistortion strains set up and the better the results in the finalreduction to powder.

It is to be understood that the above description and example areillustrative only and variations and modifications may be made thereinwithout departing from the spirit and scope of this invention. I

Having now described my invention, what I Wish to claim is:

l. A process for producing powdered magnesium which comprises coldrolling crystalline magnesium obtained by sublimation to make themagnesium brittle by mechanically extending the magnesium crystals alonga crystal axis, and disintegrating the said cold rolled magnesium byhammering, the rolling and hammering being conducted in an inertatmosphere.

2. A process for producing powdered magnesium which comprises coldrolling crystalline magnesium obtained by sublimation to make themagnesium brittle by mechanically extending the magnesium crystals alonga crystal axis, and disintegratin said cold rolled magnesium bygrinding, the rolling and grinding being conducted in an inertatmosphere.

3. A process for producing powdered magnesium which comprises rapidlycold rolling crystalline magnesium obtained by sublimation to make themagnesium brittle by mechanicallyextending the magnesium crystals alonga crystal axis, and hammering to disintegrate said cold rolledmagnesium,v the magnesium having thereon a protective surface coating oflow gravity liquid hydrocarbon.

to distort the crystals 4. A process of producing powdered magnesiumwhich comprises embrittling malleable magnesium by rapidly cold rollingthe bulk metal in a. manner to extend and distort the magnesium crystalsalong a crystal axis and then producing multiple cleavages in themagnesium crystals by subjecting the rolled metal to a hammering actionuntil magnesium powder is produced.

5. The process of claim 4 wherein the cold rolled magnesium is covered-with a protective surface coating of low specific gravity liquidhydrocarbon before being subjected to the hammering action. a

6. The process of claim 4, wherein the cold rolled metal isdisintegrated by grinding the same in an inert atmosphere.

7. The process of claim 4, wherein the magnesium powder is screened andthe coarse portion is repeatedly subjected to cold rolling and hammeringoperations until the desired state of subdivision is reached.

HAROLD P. ANDERSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Noel, article in Transactions ofAmerican Institute of Mining and Metallurgical Engineers (1938) vol.128, pages 37-41, noting particularly page 39.

